BRIEF DESCRIPTION OF THE PRIOR ART
In Gutterman U.S. Pat. No. 3,447,291, a detachable mower cutter blade is disclosed which carries a cutting plate mounted within a socket at the leading side of a rectangular plate. The operational portion of the blade is curved forwardly so as to have a concavity which, according to the patentee, enhances the cutting action of the blade by directing the grass or grain to be cut. The cutting blade of this arrangement can be quickly and easily installed by the operator of the machine without resort to the services of skilled repair personnel.
In U.S. Pat. No. 4,771,593, a flat rectangular rotary cutting blade is disclosed and, as illustrated in FIG. 7 of that patent, such a blade may carry a pair of upturned flanges which extend at an angle upwardy from the principal plane of the blade plate, and are located near opposite ends of the blade. The flanges at opposite ends of the blade are located directly behind straight cutting edges carried on the leading, opposite sides of the blade.
In U.S. Pat. No. 4,628,672, a rotary cutting blade is disclosed in which the cutting edges formed at the leading sides of the blade adjacent the opposite ends of the blade are formed in a convex configuration. This causes them to slice through the vegetation to be cut, rather than severing the vegetation with a direct shearing action. Moreover, the sharpened cutting edges of the blades at the opposite ends thereof, extend from the leading edge to the trailing edge of the blade. These convex shearing edges can also be combined with a portion of the blade sharpened along the leading edge at opposite sides thereof, and constituting conventional contact-type cutting edges. There are upturned wind flanges provided at opposite ends of the blade and located approximately directly behind the straight conventional impact cutting edges provided at the leading edges of the blade. The inclusion of the wind flanges, or fan flanges, at the trailing edges of the blade is intended to create a fanning action for lifting the cut grass and blowing such grass through an outlet in the rotary cutting blade housing.
In FIG. 7 of Jones U.S. Pat. No. 4,628,672, an upturned flange is shown as located at the rear side of the blade with this flange trailing directly behind a sharpened cutting edge. Near the outer end of the blade, the cutting edges have an indentation or concavity formed in them. Upturned portions are referred to by the patentee as "fan" or "wind" portions.
In Watson et al U.S. Pat. No. 3,214,896, a rotary cutter blade is disclosed which has concave recesses or indentations formed along the leading edge of the blade, with these being sharpened for cutting the grass or other vegetation. At the trailing edge of the blade, angular wings or flanges are turned upwardly to provide "an upward fanning action" as the blade is rotated.
Another cutting blade which has cutting edges forming concave recesses is disclosed in U.S. Pat. No. 3,022,621. It will be noted that in this patent there are also outturned flanges which function to direct grass away from the blade.
In U.S. Pat. No. 1,407,417, the patentee provides a concave sharpened cutting surface along the forward or leading side of the blade.
A similar concave cutting surface is shown in Ashbury U.S Pat. No. 2,850,862. Here the patentee states that this sharpened concavity is provided so as to achieve a "sickle cutting action".
In Phillips U.S. Pat. No. 3,087,298, the blade provided has a hook-shaped portion at each of its ends, so that the overall configuration of the blade is somewhat of an S shaped configuration The cutting edges which are provided at the convex outer side edges of each of the end portions of the blade are rounded or arcuate in configuration, and terminate at outstanding baffle plates which are also convex in terms of direction of the blade travel. These baffle plates are said to function to push aside solid obstacles in the path of the blade as well as to create a centrifugal cyclonic action directing the severed grass toward the outlet in the mower housing.
In most but not all of the blade designs employed in the prior art, the wind vanes or upturned flanges are generally triangular in configuration, and extend at an angle to the longitudinal axis of the blade.